Method of manufacturing alloy steel



Patented Aug. 30, 1938 William MacCormac Burden, Reginald Genders, and Reginald Harrison, Woolwich, London;

England, assignors to England Solal Limited, London,

N Drawing; Application April s, 1936, Serial No. 73,044. In Great Britain April 30, 1935 4 Claims. (Cl. 75-129) This invention relates to alloy steels and has for its principal object to produce alloy steels having an extremely high intrinsic hardness value such as are particularly suitable for example for 5 cutting tools.

The invention consists in a method of producing a steel containing a large amount of an extremely hard carbide which is inert to the heat treatment of the steel matrix, by adding tantalum, niobium or one or more of the elements zirconium, boron and titanium to an iron carbon melt of high carbon content such as molten pig iron, whereby the carbide of the added metal is formed by reaction with the carbon in the melt andremains as a suspension in the steel. For

the purpose of any heat treatment such as hardening by quenching, a suitable content of carbon may be left in the steel matrixby adding less of the element than is required to combine with the whole of the carbon. Steels containing carbides of tantalum, niobium, zirconium and titanium are known, but it has hitherto been the practice to manufacture such steels by forming the carbide of the metal in question and then adding it to a bath of molten steel. This is unsatisfactory because firstly the carbides are expensive and difficult to manufacture, and secondly it is not always easy to introduce them into the melt. We have found, however, that iron alloys rich in carbon, e. g. pig iron, can be converted directly into a steel suitable for the manufacture of cutting tools or of wear resisting articles by adding to the molten pig iron one or more of the elements enumerated above. The element should of course be added in a quantity sufficient to combine with the major portion of the carbon present in the pig iron, ,but, as explained above, such amount of carbon may be left uncombined as may be required to render the matrix responsive to heat treatment.

By adopting the invention, pig iron can be converted at minimum expense directly into a high quality steel; without a preliminary treatment' for removal of carbon. The added element need not necessarily be added in the elementary state, but may for example be added in the form of a compound with iron, such as ferro-tantalum, and the term elementary state as used in the appended claims includes an alloy of the said element with iron.

The steel produced by the method according to the invention has a high content of carbide of the element added to the pig iron. This carbide is not responsive to heat treatment. Moreover a it may be isolated, if desired, by chemical means for'use as an abrasive or in the manufacture of cutting tips for tools. I

Further features of the invention will be apparent from the description given hereafter, and when the expression or other element occurs herein it will be understood that such expression means one or more of the elements niobium, zirconium, boron and titanium.

In carrying our invention into effect in one convenient manner when producing an alloy steel of high hardness value for cutting tools and the like, we take a molten iron carbon alloy of high carbon content (for example white pig iron) with the addition, if necessary, of solid carbon, and to this alloy we add a quantityv of tantalum or other element suflicient to combine with all the carbon present in excess of about 0.7 per cent (this may require up to 30 or 40 per cent of the added element) and in this way we produce a carbide of tantalum or other element in suspension in a matrix of iron or steel of adjustable carbon content. The matrix may, if desired, be independently adjusted in composition v by addition to the melt of such known steel making elements as, chromium, tungsten, molybdenum etc., these elements being selected as may be suitable to produce any required mechanical properties in the matrix by heat treatment.

The invention is not to be limited to the foregoing details which are given by way of illustration only, nor is it to be confined to the particular applications given by way of example, and we may vary the proportions of the tantalum and/or other element added depending upon the purpose for which the alloys is required or any practical requirements that may have to "be fulfilled.

What we claim as our invention and desire to secure by Letters Patent is:

1. A method of manufacturing a steel suitable for cutting tools, and consisting of a relatively soft matrix of iron of low carbon content containing in suspension a high proportion of a hard carbide of one at least of the elements, tantalum, niobium, zirconium, boron, titanium, which consists in incorporating in the elementary state in molten pig iron, one at least of said elements in a total quantity of about 30 to 40% thereby effecting a direct conversion of the pig iron into the tool steel aforesaid.

2. A method of manufacturing a steel suitable for cutting tools and consisting of a relatively soft matrix of iron of low carbon content containing in suspension a high proportion of a hard carbide of one at least of the elements tan- 3. A method or manufacturing a steel suitable for cutting tools and consisting of a matrix of iron containing about 0.7% of carbon and contaming in suspension & high proportion of a, hard carbide of one at least of the elements tantalum, niobium, zirconium, boron, titanium, which consists in incorporating in the elementary state in molten pig iron one at least of said elements in a. total quantity of about so to 40%, thereby effecting direct conversion of the pig iron into the tool steel aforesaid.

w in the method of manufacturing tool steel claimed in claim the step of incorporating one of the class of steel-making elements consisting of chromium, tungsten anol'molybdenum in the matrix by addition of said elements to the melt. 3o

WHJHAR Z R IACCORMAC BURDW. REGINALD GMDERS. REGINALD HARRISON. 

